U.S. patent application number 14/700957 was filed with the patent office on 2015-08-20 for audio signal coding device and audio signal decoding device.
The applicant listed for this patent is SOCIONEXT INC.. Invention is credited to Shunji MIYASAKA, Yong Hwee SIM.
Application Number | 20150235646 14/700957 |
Document ID | / |
Family ID | 50626775 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150235646 |
Kind Code |
A1 |
MIYASAKA; Shunji ; et
al. |
August 20, 2015 |
AUDIO SIGNAL CODING DEVICE AND AUDIO SIGNAL DECODING DEVICE
Abstract
An audio signal coding device including: a layered coding unit
which codes a low-band signal which is included in an input audio
signal and in a frequency band lower than a boundary frequency to
generate a coded low-band signal, and codes a high-band signal in a
frequency band higher than the boundary frequency to generate a
coded high-band signal; and a layer boundary setting unit which
sets the boundary frequency to a first frequency if a coding
bitrate to be used by the layered coding unit for coding the
low-band signal and the high-band signal is a first bitrate, and
sets the boundary frequency to a second frequency lower than the
first frequency if the coding bitrate is a second bitrate lower
than the first bitrate.
Inventors: |
MIYASAKA; Shunji; (Osaka,
JP) ; SIM; Yong Hwee; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SOCIONEXT INC. |
Kanagawa |
|
JP |
|
|
Family ID: |
50626775 |
Appl. No.: |
14/700957 |
Filed: |
April 30, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2013/004450 |
Jul 22, 2013 |
|
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14700957 |
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Current U.S.
Class: |
381/22 ;
381/23 |
Current CPC
Class: |
G10L 19/008 20130101;
G10L 19/24 20130101; G10L 19/0204 20130101; H03M 7/3059
20130101 |
International
Class: |
G10L 19/008 20060101
G10L019/008 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2012 |
JP |
2012-240711 |
Claims
1. An audio signal coding device comprising: a layered coding unit
configured to code a low-band signal in a first frequency band
lower than a boundary frequency to generate a coded low-band
signal, and code a high-band signal in a second frequency band
higher than the boundary frequency to generate a coded high-band
signal, the low-band signal and the high-band signal being included
in an input audio signal; a layer boundary setting unit configured
to determine a coding bitrate to be used by the layered coding unit
for coding the low-band signal and the high-band signal, set the
boundary frequency to a first frequency if the coding bitrate is a
first bitrate, and set the boundary frequency to a second frequency
lower than the first frequency if the coding bitrate is a second
bitrate lower than the first bitrate; and a multiplexer unit
configured to multiplex the coded low-band signal, the coded
high-band signal, and boundary information indicative of the
boundary frequency to generate a coded audio signal.
2. The audio signal coding device according to claim 1, wherein the
multiplexer unit is configured to multiplex the coded low-band
signal and the coded high-band signal into the coded audio signal,
in a manner that the coded low-band signal and the coded high-band
signal are separatably allocated to respective regions of the coded
audio signal.
3. The audio signal coding device according to claim 2, wherein the
multiplexer unit is further configured to transmit the coded audio
signal to an audio signal decoding device through a transmission
path, the audio signal coding device further comprising a
transmission capacity estimation unit configured to estimate a
transmission capacity of the transmission path, wherein the layer
boundary setting unit is further configured to set the coding
bitrate to the first bitrate if the transmission capacity is a
first transmission capacity, set the coding bitrate to the second
bitrate if the transmission capacity is a second transmission
capacity less than the first transmission capacity, and determine
the boundary frequency using the set coding bitrate.
4. The audio signal coding device according to claim 3, wherein the
transmission path includes a first layer and a second layer having
a lower priority than the first layer, and a signal on the second
layer is discarded if an amount of transmission of the transmission
path exceeds a predetermined value, and the multiplexer unit is
configured to send the coded audio signal to the transmission path
in a manner that the coded low-band signal is allocated to the
first layer and the coded high-band signal is allocated to the
second layer.
5. The audio signal coding device according to claim 4, further
comprising: an inter-channel correlation detection unit configured
to detect a phase difference between channels of an N-channel audio
signal and a ratio between levels of the channels to generate
inter-channel correlation information indicative of the phase
difference and the ratio between the levels, where N is an integer
greater than 1; and a downmix unit configured to downmix the
N-channel audio signal into an M-channel signal to generate the
input audio signal, where M is an integer greater than 0 and
smaller than N, wherein the multiplexer unit is configured to
multiplex the coded low-band signal, the coded high-band signal,
the boundary information, and the inter-channel correlation
information to generate the coded audio signal and allocates the
inter-channel correlation information to the second layer.
6. The audio signal coding device according to claim 1, wherein the
layer boundary setting unit is further configured to: set the first
frequency band to a first band and the second frequency band to a
second band if the coding bitrate is the first bitrate; and set the
first frequency band to a third band narrower than the first band
and the second frequency band to a fourth band narrower than the
second band if the coding bitrate is the second bitrate.
7. An audio signal decoding device which decodes a coded audio
signal which is obtained by coding an input audio signal using a
layered coding scheme, the audio signal decoding device comprising:
a splitter unit configured to obtain, from the coded audio signal,
a coded low-band signal obtained by coding a low-band signal in a
first frequency band lower than a boundary frequency, a coded
high-band signal obtained by coding a high-band signal in a second
frequency band higher than the boundary frequency, and boundary
information indicative of the boundary frequency, the low-band
signal and the high-band signal being included in the input audio
signal; a low-band signal decoding unit configured to decode the
coded low-band signal to generate a decoded low-band signal; a
high-band signal decoding unit configured to decode the coded
high-band signal, according to the boundary information, to
generate a decoded high-band signal; and a combiner unit configured
to combine the decoded low-band signal and the decoded high-band
signal to generate a decoded audio signal, wherein the combiner
unit is configured to generate the decoded audio signal using the
decoded low-band signal if the combiner unit fails to obtain the
coded high-band signal.
8. The audio signal decoding device according to claim 7, wherein
the input audio signal is obtained by downmixing an N-channel audio
signal having N channels into an M-channel signal, where N is an
integer greater than 1 and M is an integer greater than 0 and less
than N, and the splitter unit is further configured to obtain, from
the coded audio signal, inter-channel correlation information
indicative of a phase difference between the N channels and a ratio
between levels of the N channels, the audio signal decoding device
further comprising an upmix unit configured to upmix the decoded
audio signal having M channels to a decoded audio signal having the
N channels, using the inter-channel correlation information.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of PCT International
Application No. PCT/JP2013/004450 filed on Jul. 22, 2013,
designating the United States of America, which is based on and
claims priority of Japanese Patent Application No. 2012-240711
filed on Oct. 31, 2012. The entire disclosures of the
above-identified applications, including the specifications,
drawings and claims are incorporated herein by reference in their
entirety.
FIELD
[0002] The present disclosure relates to an audio signal coding
device which codes an input audio signal to generate a coded audio
signal, and an audio signal decoding device which decodes the coded
audio signal.
BACKGROUND
[0003] In recent years, systems which distribute audio-video
signals through digital networks are widely used. For example, a
system, such as YouTube (registered trademark), performs a service
which distributes audio-video signals from a server installed at a
remote location. Additionally, in recent years, teleconferencing
systems which communicate quality audio-video signals has also
become popular.
[0004] While transmission capacity of a transmission path through
which digital signals as such are transmitted is increasing year by
year, an amount of transmission of audio-video signals as mentioned
above exceeds the increase in the transmission capacity. Due to
this, there is an increasing need for compression coding technique
on audio-video signals.
[0005] For example, the techniques disclosed in Patent Literatures
(PTLs) 1 and 2 are known as such compression coding techniques.
[0006] The transmission capacity of a transmission path through
which the digital signal as mentioned above is transmitted varies
from time to time. Thus, when the transmission path is congested,
audio-video signals are not transmitted in real time, thereby, in
most cases, causing gaps in a reproduced signal. For example,
skipping occurs or a screen freezes for a brief moment. A method to
solve this problem changes a bitrate in response to the variation
in transmission capacity.
CITATION LIST
Patent Literature
[0007] [PTL 1] U.S. Pat. No. 7,342,880
[0008] [PTL 2] Japanese Unexamined Patent Application Publication
No. 2009-503559
SUMMARY
Technical Problem
[0009] In such techniques, it is desired to inhibit degradation of
audio quality when the bitrate is lowered.
[0010] Thus, an object of the present disclosure is to provide an
audio signal coding device and audio signal decoding device which
can inhibit the degradation of audio quality when a bitrate is
lowered.
Solution to Problem
[0011] An audio signal coding device according to an aspect of the
present disclosure includes: a layered coding unit configured to
code a low-band signal in a first frequency band lower than a
boundary frequency to generate a coded low-band signal, and code a
high-band signal in a second frequency band higher than the
boundary frequency to generate a coded high-band signal, the
low-band signal and the high-band signal being included in an input
audio signal; a layer boundary setting unit configured to determine
a coding bitrate to be used by the layered coding unit for coding
the low-band signal and the high-band signal, set the boundary
frequency to a first frequency if the coding bitrate is a first
bitrate, and set the boundary frequency to a second frequency lower
than the first frequency if the coding bitrate is a second bitrate
lower than the first bitrate; and a multiplexer unit configured to
multiplex the coded low-band signal, the coded high-band signal,
and boundary information indicative of the boundary frequency to
generate a coded audio signal.
[0012] According to the above configuration, the audio signal
coding device can broaden the reproduction band even if the coding
bitrate is lowered. As such, the audio signal coding device can
inhibit degradation of the audio quality when the bitrate is
lowered.
[0013] For example, the multiplexer unit may multiplex the coded
low-band signal and the coded high-band signal into the coded audio
signal, in a manner that the coded low-band signal and the coded
high-band signal are separatably allocated to respective regions of
the coded audio signal.
[0014] According to the above configuration, the audio signal
coding device discards the coded high-band signal, thereby reducing
the bitrate.
[0015] For example, the multiplexer unit may further transmit the
coded audio signal to an audio signal decoding device through a
transmission path, the audio signal coding device further including
a transmission capacity estimation unit configured to estimate a
transmission capacity of the transmission path, wherein the layer
boundary setting unit may further set the coding bitrate to the
first bitrate if the transmission capacity is a first transmission
capacity, set the coding bitrate to the second bitrate if the
transmission capacity is a second transmission capacity less than
the first transmission capacity, and determine the boundary
frequency using the set coding bitrate.
[0016] According to the above configuration, in environment where
the transmission capacity of the transmission path varies from time
to time, the audio signal coding device can change the coding
bitrate, in response to the variation in transmission capacity.
[0017] For example, the transmission path may include a first layer
and a second layer having a lower priority than the first layer,
and a second layer signal may be discarded if an amount of
transmission of the transmission path exceeds a predetermined
value, and the multiplexer unit may send the coded audio signal to
the transmission path in a manner that the coded low-band signal is
allocated to the first layer and the coded high-band signal is
allocated to the second layer.
[0018] According to the above configuration, if the transmission
capacity of the transmission path is scarce, the audio signal
coding device discards the coded high-band signal, thereby reducing
the bitrate.
[0019] For example, the audio signal coding device may further
include: an inter-channel correlation detection unit configured to
detect a phase difference between channels of an N-channel audio
signal and a ratio between levels of the channels to generate
inter-channel correlation information indicative of the phase
difference and the ratio between the levels, where N is an integer
greater than 1; and a downmix unit configured to downmix the
N-channel audio signal into an M-channel signal to generate the
input audio signal, where M is an integer greater than 0 and
smaller than N, wherein the multiplexer unit may multiplex the
coded low-band signal, the coded high-band signal, the boundary
information, and the inter-channel correlation information to
generate the coded audio signal and allocates the inter-channel
correlation information to the second layer.
[0020] According to the above configuration, if the transmission
capacity of the transmission path is scarce, the audio signal
coding device discards the inter-channel correlation information,
thereby reducing the bitrate.
[0021] For example, the layer boundary setting unit may further:
set the first frequency band to a first band and the second
frequency band to a second band if the coding bitrate is the first
bitrate; and set the first frequency band to a third band narrower
than the first band and the second frequency band to a fourth band
narrower than the second band if the coding bitrate is the second
bitrate.
[0022] According to the above configuration, the audio signal
coding device can reduce the bitrate, if the transmission capacity
of the transmission path is scarce.
[0023] Moreover, an audio signal decoding device according to an
aspect of the present disclosure may be an audio signal decoding
device which decodes a coded audio signal which is obtained from
coding an input audio signal using a layered coding scheme, the
audio signal decoding device including: a splitter unit configured
to obtain, from the coded audio signal, a coded low-band signal
obtained by coding a low-band signal in a first frequency band
lower than a boundary frequency, a coded high-band signal obtained
by coding a high-band signal in a second frequency band higher than
the boundary frequency, and boundary information indicative of the
boundary frequency, the low-band signal and the high-band signal
being included in the input audio signal; a low-band signal
decoding unit configured to decode the coded low-band signal to
generate a decoded low-band signal; a high-band signal decoding
unit configured to decode the coded high-band signal, according to
the boundary information, to generate a decoded high-band signal;
and a combiner unit configured to combine the decoded low-band
signal and the decoded high-band signal to generate a decoded audio
signal, wherein the combiner unit may generate the decoded audio
signal using the decoded low-band signal if the combiner unit fails
to obtain the coded high-band signal.
[0024] According to the above configuration, the audio signal
decoding device can reproduce an audio signal without audio
discontinuities, even if the transmission capacity of the
transmission path is scarce.
[0025] For example, the input audio signal may be obtained by
downmixing an N-channel audio signal having N channels into an
M-channel signal, where N is an integer greater than 1 and M is an
integer greater than 0 and less than N, and the splitter unit may
further obtain, from the coded audio signal, inter-channel
correlation information indicative of a phase difference between
the N channels and a ratio between levels of the N channels, the
audio signal decoding device further including an upmix unit
configured to upmix the decoded audio signal having M channels to a
decoded audio signal having the N channels, using the inter-channel
correlation information.
[0026] According to the above configuration, the audio signal
decoding device can reproduce an audio signal without audio
discontinuities, even if the transmission capacity of the
transmission path is scarce.
[0027] These general and specific aspects may be implemented in a
system, a method, an integrated circuit, a computer program, or a
computer-readable recording medium such as a CD-ROM, or any
combination of systems, methods, integrated circuits, computer
programs, or computer-readable recording media.
Advantageous Effects
[0028] The present disclosure can provide the audio signal coding
device and the audio signal decoding device which can inhibit
degradation of audio quality when the bitrate is lowered.
BRIEF DESCRIPTION OF DRAWINGS
[0029] These and other objects, advantages and features of the
disclosure will become apparent from the following description
thereof taken in conjunction with the accompanying drawings that
illustrate a specific embodiment of the present disclosure.
[0030] FIG. 1 is a block diagram showing a configuration of an
audio signal coding device according to a comparative example 1 of
the present disclosure.
[0031] FIG. 2 is a diagram illustrating a method of switching
between coding schemes in the audio signal coding device according
to the comparative example 1 of the present disclosure.
[0032] FIG. 3 is a block diagram showing a configuration of an
audio signal transmission system according to a comparative example
2 of the present disclosure.
[0033] FIG. 4 is a diagram showing transitions in code amount and
in frequency band of a coded audio signal according to the
comparative example 2 of the present disclosure.
[0034] FIG. 5 is a block diagram showing a configuration of an
audio signal transmission system according to an embodiment 1 of
the present disclosure.
[0035] FIG. 6 is a block diagram showing a configuration of an
audio signal coding device according to the embodiment 1 of the
present disclosure.
[0036] FIG. 7 is a block diagram showing a configuration of an
audio signal decoding device according to the embodiment 1 of the
present disclosure.
[0037] FIG. 8 is a diagram showing boundary frequencies in response
to transmission capacity according to the embodiment 1 of the
present disclosure.
[0038] FIG. 9 is a diagram showing transitions in code amount and
in frequency band of a coded audio signal according to the
embodiment 1 of the present disclosure.
[0039] FIG. 10 is a flowchart illustrating a coding process
performed by the audio signal coding device according to the
embodiment 1 of the present disclosure.
[0040] FIG. 11 is a flowchart illustrating a decoding process
performed by the audio signal decoding device according to the
embodiment 1 of the present disclosure.
[0041] FIG. 12 is a block diagram showing a configuration of an
audio signal coding device according to an embodiment 2 of the
present disclosure.
[0042] FIG. 13 is a block diagram showing a configuration of an
audio signal decoding device according to the embodiment 2 of the
present disclosure.
[0043] FIG. 14 is a flowchart illustrating a coding process
performed by the audio signal coding device according to the
embodiment 2 of the present disclosure.
[0044] FIG. 15 is a flowchart illustrating a decoding process
performed by the audio signal decoding device according to the
embodiment 2 of the present disclosure.
DESCRIPTION OF EMBODIMENTS
[0045] First, prior to describing an audio signal coding device
according to embodiments of the present disclosure, audio signal
coding devices according to comparative examples 1 and 2 of the
present disclosure will be set forth.
[0046] As described above, the transmission capacity of a
transmission path through which the digital signal is transmitted
varies from time to time. Thus, when the transmission path is
congested, audio-video signals are not transmitted in real time,
thereby, in most cases, causing gaps in a reproduced signal. For
example, skipping occurs or a screen freezes for a brief
moment.
[0047] To avoid this, a technique may be employed which estimates
the variation in transmission capacity of the transmission path. In
this technique, audio-video signals are transmitted at high
bitrates when the transmission capacity is large to ensure high
image quality and high audio quality, and when the transmission
capacity is small, the audio-video signals are transmitted at low
bitrates to avoid a reproduced signal skipping and freezing of the
image.
[0048] FIG. 1 is a diagram showing an example of the audio signal
coding device according to the comparative example 1 of the present
disclosure. An audio signal coding device 500 shown in FIG. 1
includes a multi-rate coding unit 501, a transmission capacity
estimation unit 502, and a coding scheme selection unit 503.
[0049] The multi-rate coding unit 501 codes an input audio signal
510, selectively using one of a plurality of bitrates, to generate
a coded audio signal 511. For example, the multi-rate coding unit
501 codes the input audio signal 510 at a bitrate from 24 kbps to
192 kbps. The input audio signal 510 is a stereo signal, for
example.
[0050] FIG. 2 is a diagram illustrating a method of selecting a
coding scheme. As illustrated in FIG. 2, if the bitrate is low the
multi-rate coding unit 501 converts the input audio signal 510 into
a monophonic signal and then codes it. If the bitrate is high the
multi-rate coding unit 501 codes the input audio signal 510 in the
form of a stereo signal. Moreover, if the bitrate is low the
multi-rate coding unit 501 compression codes the input audio signal
510 by G.722, and if the bitrate is high, compression codes the
input audio signal 510 by advance audio coding (AAC). Then, the
coded audio signal 511 generated by the compression coding is
transmitted through a transmission path 504.
[0051] The transmission capacity of the transmission path 504
varies from time to time. The transmission capacity estimation unit
502 estimates the transmission capacity that varies from time to
time. It should be noted that specific methods of the processing of
estimating the transmission capacity may include a variety of known
methods.
[0052] The coding scheme selection unit 503 determines the bitrate
for audio coding, according to the transmission capacity estimated
by the transmission capacity estimation unit 502, and selects a
coding scheme that corresponds to the determined bitrate.
Specifically, the coding scheme selection unit 503 selects the
number of channels (stereo or monophonic) and a compression scheme
(AAC or G.722) for a signal to be coded in response to the bitrate.
Then, the multi-rate coding unit 501 compression codes the input
audio signal 510 using the selected coding scheme.
[0053] According to the above configuration, a best-suited coding
scheme is selected in response to the transmission capacity that
varies from time to time. This allows the audio signal coding
device 500 to code the input audio signal 510 at high audio quality
when the transmission capacity permits. When the transmission
capacity is scarce, the audio signal coding device 500 can transmit
an audio signal that has no sound break, although at a degraded
audio quality.
[0054] In such a method as described above, however, the number of
channels of a signal to be coded and the compression scheme changes
with the variation in bitrate, which may cause a moment where a
reproduced signal does not continue seamlessly. For example, at 192
kbps, the signal is coded by stereo AAC, and at 64 kbps, the signal
is coded by monophonic AAC. This causes discontinuities where the
reproduction audio switches from stereo to monophonic. Furthermore,
at 32 kbps, the signal is coded by monophonic G.722. Thus,
discontinuities are caused where the compression scheme switches in
the reproduction audio.
[0055] The following technique can be used to solve the above
problem.
[0056] FIG. 3 is a block diagram showing a configuration of an
audio signal transmission system according to the comparative
example 2 of the present disclosure.
[0057] An audio signal transmission system 600 shown in FIG. 3
includes an audio signal coding device 700, an audio signal
decoding device 800, and a transmission path 900.
[0058] The audio signal coding device 700 codes an input audio
signal 750 to generate a coded audio signal 760. The audio signal
coding device 700 includes a splitter unit 711, a low-band signal
coding unit 712, a high-band signal coding unit 713, and a
multiplexer unit 702.
[0059] The splitter unit 711 splits the input audio signal 750 into
two frequency band signals to generate a low-band signal 751 and a
high-band signal 752. The low-band signal coding unit 712 codes the
low-band signal 751 to generate a coded low-band signal 753. The
high-band signal coding unit 713 codes the high-band signal 752 to
generate a coded high-band signal 754. The multiplexer unit 702
multiplexes the coded low-band signal 753 and the coded high-band
signal 754 to generate the coded audio signal 760. The coded audio
signal 760 is transmitted through the transmission path 900. Here,
the coded low-band signal 753 is allocated to a high priority layer
of the transmission path 900 and transmitted, and the coded
high-band signal 754 is allocated to a low priority layer of the
transmission path 900 and transmitted.
[0060] The audio signal decoding device 800 receives the coded
audio signal 760 transmitted through the transmission path 900.
Then, the audio signal decoding device 800 decodes the coded audio
signal 760 to generate a decoded audio signal 850. The audio signal
decoding device 800 includes a splitter unit 801, a low-band signal
decoding unit 811, a high-band signal decoding unit 812, and a
combiner unit 813.
[0061] The splitter unit 801 splits the coded audio signal 760 into
a coded low-band signal 851 and a coded high-band signal 852. The
low-band signal decoding unit 811 decodes the coded low-band signal
851 to generate a decoded low-band signal 854. The high-band signal
decoding unit 812 decodes the coded high-band signal 852 to
generate a decoded high-band signal 855. The combiner unit 813
combines the decoded low-band signal 854 and the decoded high-band
signal 855 to generate the decoded audio signal 850 which is a
pulse code modulation (PCM) signal.
[0062] Here, as described above, the coded low-band signal 753 is
allocated to the high priority layer of the transmission path 900
and transmitted, and the coded high-band signal 754 is allocated to
the low priority layer of the transmission path 900 and
transmitted. This is so that the coded high-band signal 754
allocated to the low priority layer of the transmission path 900 is
not transmitted if the transmission capacity of the transmission
path 900 is scarce. For example, as shown in (a) of FIG. 4, if the
transmission capacity permits (large transmission capacity), both
the coded low-band signal 753 and the coded high-band signal 754
are transmitted. On the other hand, if the transmission capacity
does not permit (small transmission capacity), only the coded
low-band signal 753 is transmitted.
[0063] If the coded high-band signal 754 (852) is not transmitted,
the high-band signal decoding unit 812 outputs, as the decoded
high-band signal 855, a zero signal or a signal that mimics a
high-band signal.
[0064] By so doing, the coded signal is layered, and transmitted in
a prioritized manner. Thus, the occurrence of discontinuities in
audio with change in the number of channels or change of the coding
scheme as indicated in the comparative example 1 can be prevented
even if the transmission capacity varies.
[0065] As described above, the audio signal transmission system 600
according to the comparative example 2 drops the coded high-band
signal 754 when the transmission capacity is scarce due to the
congestion of the transmission path 900. However, the size (code
amount) of the coded high-band signal 754 is smaller than that of
the coded low-band signal 753, and thus the effect of reduction in
amount of information to be transmitted, which is obtained by
dropping the coded high-band signal 754, is small. In view of this
the inventors have found a problem that this processing does not
sufficiently contribute to mitigate the congestion of the
transmission path 900.
[0066] The inventors have also found that the audio quality
significantly degrades if the coded high-band signal 754 is dropped
because all high-band components (frequency bands above 1/2 of the
reproduction band) are dropped. Here, (a) of FIG. 4 shows
transitions in code amount with the variation in transmission
capacity. Part (b) of FIG. 4 shows reproduction bands (frequency
bands reproduced) with the variation in transmission capacity. As
shown in FIG. 4, a wide-band signal is reproduced if the
transmission capacity of the transmission path 900 permits,
whereas, only a narrow-band signal is reproduced suddenly if the
transmission capacity of the transmission path 900 is scarce.
[0067] Hereinafter, embodiments according to the present disclosure
will be described in details, with reference to the accompanying
drawings. It should be noted that embodiments described below are
generic and specific illustration of the present disclosure.
Values, shapes, materials, components, arrangement or connection
between the components, steps, and the order of the steps are
merely illustrative and not intended to limit the present
disclosure. Moreover, among components of the embodiments below,
components not set forth in the independent claims indicating the
top level concept of the present disclosure will be described as
optional components.
EMBODIMENT 1
[0068] Hereinafter, an audio signal coding device and audio signal
decoding device according to an embodiment 1 of the present
disclosure will be described, with reference to the accompanying
drawings.
[0069] The audio signal coding device according to the present
embodiment changes a boundary frequency which is used in signal
splitting, in response to a transmission capacity of a transmission
path. This allows the audio signal coding device to appropriately
correspond to the variation in transmission capacity of the
transmission path.
[0070] First, a configuration of an audio signal transmission
system 100 according to the present embodiment will be
described.
[0071] FIG. 5 is a block diagram showing a configuration of the
audio signal transmission system 100 according to the present
embodiment. The audio signal transmission system 100 shown in FIG.
1 includes an audio signal coding device 200 (a transmitting
device), an audio signal decoding device 300 (a receiving device),
and a transmission path 400.
[0072] The audio signal coding device 200 codes an input audio
signal 250 to generate a coded audio signal 260. Then, the audio
signal coding device 200 transmits the coded audio signal 260 to
the audio signal decoding device 300 through the transmission path
400.
[0073] The audio signal decoding device 300 receives the coded
audio signal 260, and decodes the coded audio signal 260 to
generate a decoded audio signal 350.
[0074] In the following, a configuration of the audio signal coding
device 200 will be described.
[0075] FIG. 6 is a block diagram showing a configuration of the
audio signal coding device 200 according to the present embodiment.
The audio signal coding device 200 shown in FIG. 6 includes a
layered coding unit 201, a multiplexer unit 202, a transmission
capacity estimation unit 203, and a layer boundary setting unit
204.
[0076] The layered coding unit 201 splits the input audio signal
250 into two frequency band signals and codes the signals in a
layered manner. Specifically, the layered coding unit 201 codes a
low-band signal 251, which is included in the input audio signal
250 and in a first frequency band lower than a boundary frequency,
to generate a coded low-band signal 253. The layered coding unit
201 also codes a high-band signal 252, which is included in the
input audio signal 250 and in a second frequency band higher than
the boundary frequency, to generate a coded high-band signal 254.
The layered coding unit 201 includes a splitter unit 211, a
low-band signal coding unit 212, and a high-band signal coding unit
213. The splitter unit 211 splits the input audio signal 250 into
at least two frequency band signals. For example, the splitter unit
211 splits the input audio signal 250 into the low-band signal 251
and the high-band signal 252. The low-band signal coding unit 212
codes the low-band signal 251 to generate the coded low-band signal
253. The high-band signal coding unit 213 codes the high-band
signal 252 to generate the coded high-band signal 254.
[0077] The multiplexer unit 202 multiplexes the coded low-band
signal 253, the coded high-band signal 254, and boundary
information 255 described below to generate the coded audio signal
260. The multiplexer unit 202 multiplexes the coded low-band signal
253 and the coded high-band signal 254 in a manner that the coded
low-band signal 253 and the coded high-band signal 254 are
separatably allocated to respective regions of the coded audio
signal 260.
[0078] The coded audio signal 260 generated by the multiplexer unit
202 is transmitted through the transmission path 400. Here, the
multiplexer unit 202 allocates the coded low-band signal 253 to a
high priority layer (a first layer) of the transmission path 400
and the coded high-band signal 254 to a low priority layer (a
second layer) of the transmission path 400 to send the coded audio
signal 260 to the transmission path 400.
[0079] Here, the transmission path 400 has the first layer and the
second layer having a lower priority than the first layer, and
discards a signal on the second layer if an amount of transmission
of the transmission path 400 exceeds a predetermined value.
[0080] The transmission capacity estimation unit 203 estimates the
transmission capacity of the transmission path 400.
[0081] In response to the transmission capacity estimated by the
transmission capacity estimation unit 203, the layer boundary
setting unit 204 determines a frequency band signal to be handled
as the low-band signal 251 and a frequency band signal to be
handled as the high-band signal 252.
[0082] Specifically, the transmission capacity estimation unit 203
determines the above-mentioned boundary frequency. More
specifically, the layer boundary setting unit 204 determines a
coding bitrate to be used in coding signals by the layered coding
unit 201. If the coding bitrate is a first bitrate, the layer
boundary setting unit 204 sets the boundary frequency to a first
frequency, and, if the coding bitrate is a second bitrate lower
than the first bitrate, sets the boundary frequency to a second
frequency lower than the first frequency. In other words, the lower
the coding bitrate is the lower the layer boundary setting unit 204
sets the boundary frequency.
[0083] The layer boundary setting unit 204 may determine the
above-mentioned coding bitrate, in response to a transmission
capacity of the transmission path 400. Specifically, if the
transmission capacity is a first transmission capacity, the layer
boundary setting unit 204 sets the coding bitrate to the first
bitrate, and, if the transmission capacity is a second transmission
capacity less than the first transmission capacity, sets the coding
bitrate to the second bitrate lower than the first bitrate. In
other words, the less the transmission capacity is the lower the
layer boundary setting unit 204 sets the coding bit. The layer
boundary setting unit 204 also sets the boundary frequency, using
the determined coding bitrate.
[0084] In other words, the layer boundary setting unit 204
determines the boundary frequency, in response to a transmission
capacity of the transmission path 400. In other words, if the
transmission capacity is the first transmission capacity the layer
boundary setting unit 204 sets the boundary frequency to the first
frequency, and, if the transmission capacity is the second
transmission capacity less than the first transmission capacity,
sets the boundary frequency to the second frequency lower than the
first frequency.
[0085] The layer boundary setting unit 204 also generates the
boundary information 255 indicating the boundary frequency, and
outputs the boundary information 255 to the multiplexer unit
202.
[0086] Moreover, the layer boundary setting unit 204 may change a
frequency band of a signal to be coded, in response to the coding
bitrate or the transmission capacity. Specifically, if the coding
bitrate is the first bitrate, the layer boundary setting unit 204
sets the first frequency band of the low-band signal 251 to a first
band and sets the second frequency band of the high-band signal 252
to a second band . If the coding bitrate is the second bitrate
lower than the first bitrate, the layer boundary setting unit 204
sets the first frequency band of the low-band signal 251 to a third
band narrower than the first band, and sets the second frequency
band of the high-band signal 252 to a fourth band narrower than the
second band. In other words, the lower the coding bitrate is (the
less the transmission capacity is) the narrower the layer boundary
setting unit 204 sets the frequency bands of the low-band signal
251 and the high-band signal 252 which are to be coded. It should
be noted that the layer boundary setting unit 204 may set, narrow,
the frequency band of one of the low-band signal 251 and the
high-band signal 252 to be coded, in response to the coding bitrate
or the transmission capacity.
[0087] Next, a configuration of the audio signal decoding device
300 will be described.
[0088] FIG. 7 is a block diagram showing a configuration of the
audio signal decoding device 300 according to the present
embodiment. The audio signal decoding device 300 shown in FIG. 7
includes a splitter unit 301 and a layered decoding unit 302.
[0089] The splitter unit 301 obtains a coded low-band signal 351, a
coded high-band signal 352, and boundary information 353 from the
coded audio signal 260 received through the transmission path 400.
Here, the coded low-band signal 351, the coded high-band signal
352, and the boundary information 353 correspond to the coded
low-band signal 253, the coded high-band signal 254, and the
boundary information 255, respectively, which are generated by the
audio signal coding device 200. In other words, the coded low-band
signal 351 is a signal obtained by coding the low-band signal 251
which is included in the input audio signal 250 and in the first
frequency band lower than the boundary frequency. The coded
high-band signal 352 is a signal obtained by coding the high-band
signal 252 which is included in the input audio signal 250 and in
the second frequency band higher than the boundary frequency. The
boundary information 353 is information indicative of the boundary
frequency.
[0090] The layered decoding unit 302 decodes the coded low-band
signal 351 and the coded high-band signal 352 using the boundary
information 353 to generate the decoded audio signal 350. The
layered decoding unit 302 includes a low-band signal decoding unit
311, a high-band signal decoding unit 312, and a combiner unit
313.
[0091] The low-band signal decoding unit 311 decodes the coded
low-band signal 351 using the boundary information 353 to generate
a decoded low-band signal 354. The high-band signal decoding unit
312 decodes the coded high-band signal 352 using the boundary
information 353 to generate a decoded high-band signal 355. It
should be noted that the boundary information 353 may be used by
either one of the low-band signal decoding unit 311 and the
high-band signal decoding unit 312.
[0092] The combiner unit 313 combines the decoded low-band signal
354 and the decoded high-band signal 355 to generate the decoded
audio signal 350 which is a PCM signal. If failed to obtain the
coded high-band signal 352, the combiner unit 313 generates the
decoded audio signal 350, using the decoded low-band signal
354.
[0093] Operation of the audio signal coding device 200 and the
audio signal decoding device 300 configured as described above will
be described below.
[0094] First, operation of the audio signal coding device 200 will
be described.
[0095] The splitter unit 211 splits the input audio signal 250 into
a plurality of frequency band signals. For example, the splitter
unit 211 splits the input audio signal 250 into 64 frequency-band
split signals.
[0096] Next, the low-band signal coding unit 212 codes a plurality
of low-band split signals among the plurality of split signals
generated by the splitter unit 211 to generate the coded low-band
signal 253. Specifically, the low-band signal coding unit 212 codes
a plurality of split signals in low frequency bands (corresponding
to the low-band signal 251 mentioned above) among the 64 split
signals. It should be noted that which frequency band signal the
low-band signal coding unit 212 is to code is determined by the
layer boundary setting unit 204.
[0097] Meanwhile, the high-band signal coding unit 213 codes a
plurality of high-band split signals among the plurality of split
signals generated by the splitter unit 211 to generate the coded
high-band signal 254. Specifically, the high-band signal coding
unit 213 codes a plurality of split signals in high frequency bands
(corresponding to the high-band signal 252 mentioned above) among
the 64 split signals. It should be noted that which frequency band
signal the high-band signal coding unit 213 is to code is
determined by the layer boundary setting unit 204. Details of the
operation will be described below.
[0098] The multiplexer unit 202 multiplexes the coded low-band
signal 253, the coded high-band signal 254, and the boundary
information 255 to generate the coded audio signal 260. The coded
audio signal 260 is transmitted through the transmission path 400.
Here, as described above, the coded low-band signal 253 is
allocated to the high priority layer of the transmission path 400
and transmitted, and the coded high-band signal 254 is allocated to
the low priority layer of the transmission path 400 and
transmitted. This is so that the coded high-band signal 254
allocated to the low priority layer is not transmitted if the
transmission capacity of the transmission path 400 is scarce.
[0099] Here, since the transmission capacity of the transmission
path 400 is a variable one, the coded audio signal 260 is rapidly
transmitted in a time period where the transmission capacity
permits, even if the bitrate is high. Therefore, audio
discontinuities do not occur, for example. There is thus no problem
in that the bitrate is high. On the other hand, in a time period
where the transmission capacity is scarce, the bitrate of the coded
audio signal 260 need be low. Thus, the transmission capacity
estimation unit 203 estimates the transmission capacity of the
transmission path 400 that varies from time to time as such. The
method of estimating the transmission capacity may be any that is
conventionally known.
[0100] In response to the transmission capacity estimated by the
transmission capacity estimation unit 203, the layer boundary
setting unit 204 determines a boundary frequency which is a
boundary between the frequency band of the low-band signal 251 to
be coded by the low-band signal coding unit 212 and the frequency
band of the high-band signal 252 to be coded by the high-band
signal coding unit 213.
[0101] FIG. 8 is a diagram illustrating an outline of a process of
determining the boundary frequency.
[0102] For example, if the transmission capacity is large, as shown
in (a) of FIG. 8, the layer boundary setting unit 204 sets the
boundary frequency to a frequency at 1/2 of the reproduction band
of the input audio signal 250. If the transmission capacity is
small, as shown in (b) of FIG. 8, the layer boundary setting unit
204 sets the boundary frequency to a frequency at 1/3 of the
reproduction band of the input audio signal 250, for example. If
the transmission capacity is even smaller, as shown in (c) of FIG.
8, the layer boundary setting unit 204 sets the boundary frequency
to a frequency at 1/4 of the reproduction band of the input audio
signal 250, for example. It should be noted that values, 1/2, 1/3,
and 1/4 mentioned here are merely illustrative and may be
appropriately determined in accordance with the magnitude of the
transmission capacity.
[0103] In the following, the operation of the low-band signal
coding unit 212 and the high-band signal coding unit 213 will be
described in detail. First, a specific example operation of the
low-band signal coding unit 212 will be described.
[0104] The low-band signal coding unit 212 codes lowest 32 split
signals among the 64 split signals generated by the splitter unit
211 if the boundary frequency is the frequency at 1/2 of the
reproduction band. Although any method may be employed for coding
signals, for example, the low-band signal coding unit 212 performs
band synthesis on the 32 split signals to generate time-domain
signals, and codes the generated time-domain signals by MPEG
standards AAC.
[0105] If the boundary frequency is the frequency at 1/3 of the
reproduction band, the low-band signal coding unit 212 codes lowest
21 split signals among the 64 split signals. Although any method
may be employed for coding signals, for example, the low-band
signal coding unit 212 performs the band synthesis on the lowest 32
split signals to generate time-domain signals as with the case
where the boundary frequency is the frequency at 1/2 of the
reproduction band. Then, the low-band signal coding unit 212 codes
the generated time-domain signals by MPEG standards AAC. Here,
since the 32 split signals has undergone the band synthesis, the
frequency band of the generated time-domain signals is 1/2 of the
frequency band of the original input audio signal 250. Thus, the
low-band signal coding unit 212 codes, among the generated
time-domain signals, time-domain signals in 2/3 of the frequency
band of the generated time-domain signals by AAC. The functionality
of AAC is used which codes an arbitrary frequency band of the input
signal.
[0106] Furthermore, if the boundary frequency is the frequency at
1/4 of the reproduction band, the low-band signal coding unit 212
codes lowest 16 split signals among the 64 split signals. Although
any method may be employed for coding signals, for example, the
low-band signal coding unit 212 performs the band synthesis on the
lowest 32 split signals to generate time-domain signals as with the
case where the boundary frequency is the frequency at 1/2 of the
reproduction band. Then, the low-band signal coding unit 212 codes
the generated time-domain signals by MPEG standards AAC. Here,
since the 32 split signals has undergone the band synthesis, the
frequency band of the generated time-domain signals is 1/2 of the
frequency band of the original input audio signal 250. Thus, the
low-band signal coding unit 212 codes, among the generated
time-domain signals, time-domain signals in 1/2 of the frequency
band of the generated time-domain signals by AAC. As described
above, the functionality of AAC is used which codes an arbitrary
frequency band of the input signal.
[0107] Next, a specific example operation of the high-band signal
coding unit 213 will be described. If the boundary frequency is the
frequency at 1/2 of the reproduction band, the high-band signal
coding unit 213 codes highest 32 split signals among the 64 split
signals. Although any method may be employed for coding signals,
for example, the high-band signal coding unit 213 employs spectral
band replication (SBR) technology. SBR is standardized as a
high-efficiency advanced audio coding (HEAAC) scheme, which
replicates and shapes a low-band frequency signal into a high-band
frequency signal, thereby coding a wideband signal at a small
bitrate. In the present embodiment, the high-band signal coding
unit 213 uses the aforementioned low-band signal 251, which has
been coded by AAC, as a low-band frequency signal to replicate and
shape the low-band frequency signal into a high-band frequency
signal, thereby coding the high-band signal 252. In other words,
the high-band signal coding unit 213 codes information as to which
band signal in the low-band signal 251 is to be replicated and how
it is shaped, thereby coding the high-band signal 252 using small
code amount.
[0108] Moreover, if the boundary frequency is the frequency at 1/3
of the reproduction band, the high-band signal coding unit 213
codes, among the 64 split signals, signals above the band of the
21st lowest band signal. In other words, the high-band signal
coding unit 213 codes the highest 43 band signals among the 64
split signals. Although any method may be employed for coding
signals, again, SBR may be employed. In the present embodiment,
using the aforementioned low-band signal 251 (21 band signals)
coded by AAC as a low-band signal, the high-band signal coding unit
213 replicates and shapes the low-band signal, thereby coding the
high-band signal 252. In this case, 43 high-band split signals need
not necessarily be coded, and signals covering about 2/3 of the
frequency band of the input audio signal 250 may be coded.
Moreover, if the boundary frequency is the frequency at 1/4 of the
reproduction band, the high-band signal coding unit 213 codes,
among the 64 split signals, signals above the band of the 16th
lowest band signal. In other words, the high-band signal coding
unit 213 codes the highest 48 band signals among the 64 split
signals. Although any method may be employed for coding signals,
again, SBR may be employed. In the present embodiment, using the
aforementioned low-band signal 251 (16 band signals) coded by AAC
as a low-band signal, the high-band signal coding unit 213
replicates and shapes the low-band signal, thereby coding the
high-band signal 252. In this case, 48 high-band split signals need
not necessarily be coded, and signals covering about 1/2 of the
frequency band of the input audio signal 250 may be coded.
[0109] In the present embodiment, the boundary information 255
generated by the layer boundary setting unit 204 is information
which indicates which band signal is to be coded by AAC and which
band signal is to be coded by SBR. The boundary information 255 is
used on the decoding side and thus the multiplexer unit 202
multiplexes the boundary information 255 to generate the coded
audio signal 260.
[0110] Then, the coded audio signal 260 is transmitted through the
transmission path 400.
[0111] Next, operation of the audio signal decoding device 300 will
be described.
[0112] The splitter unit 301 splits the coded audio signal 260
transmitted through the transmission path 400 into the coded
low-band signal 351 obtained by coding the low-band signal, the
coded high-band signal 352 obtained by coding the high-band signal,
and the boundary information 353.
[0113] The low-band signal decoding unit 311 decodes the coded
low-band signal 351 to generate the decoded low-band signal 354.
The high-band signal decoding unit 312 decodes the coded high-band
signal 352 to generate the decoded high-band signal 355. Here, the
low-band signal decoding unit 311 and the high-band signal decoding
unit 312 obtain information as to a boundary between the low band
and the high band from the boundary information 353 indicating a
layer boundary.
[0114] The combiner unit 313 combines the decoded low-band signal
354 and the decoded high-band signal 355 to generate the decoded
audio signal 350 which is a PCM signal.
[0115] FIG. 9 is a diagram showing examples of transitions in code
amount for the coded audio signal 260 generated by the series of
processing as described above ((a) of FIG. 9), and transitions in
frequency band of the decoded audio signal 350 reproduced on the
decoding side ((b) of FIG. 9).
[0116] In a time slot 1, the transmission capacity of the
transmission path 400 is adequate (large transmission capacity),
and the coded low-band signal 253 and the coded high-band signal
254 are allocated sufficient code amounts. As previously mentioned,
the coded low-band signal 253 has been coded by AAC and the coded
high-band signal 254 has been coded by SBR. Thus, the code amount
for the coded low-band signal 253 is large while the code amount
for the coded high-band signal 254 is small. As shown in (b) of
FIG. 9, the audio signal decoding device 300 can reproduce a
full-band signal.
[0117] In a time slot 2, the transmission capacity of the
transmission path 400 is becoming scarce (intermediate transmission
capacity). In this case, the audio signal coding device 200
somewhat lowers the layer boundary (the boundary frequency) to
reduce the code amount for the coded low-band signal 253. Since the
code amount for the coded low-band signal 253 is originally large,
slightly lowering the layer boundary allows large reduction in code
amount. On the other hand, the code amount for the coded high-band
signal 254 is originally small. Thus, the coded high-band signal
254 is allocated sufficient code amount in the time slot 2 as well.
As a result, as shown in (b) of FIG. 9, the reproduction band of
the signal reproduced by the audio signal decoding device 300 is
not greatly compromised. For example, comparison is made with the
example illustrated in FIG. 4. In the period where the transmission
capacity is small in FIG. 4, the reproduction band is about half of
a normal state (large transmission capacity). On the other hand, in
the time slot 2 shown in FIG. 9, the reproduction band is half or
more of the normal state while the total code amount is similar to
that illustrated in FIG. 4. In other words, a decrease in
reproduction band when the bitrate is lowered is reduced.
[0118] In a time slot 3, the transmission capacity of the
transmission path 400 is becoming further scarce (small
transmission capacity). In this case, the audio signal coding
device 200 lowers the layer boundary a little further to reduce the
code amount for the coded low-band signal 253. The code amount for
the coded low-band signal 253 is originally large, and thus further
lowering the layer boundary reduces large code amount. On the other
hand, the code amount for the coded high-band signal 254 slightly
reduces in the time slot 3 as well, even though the code amount for
the coded high-band signal 254 is originally small. This is because
the band of the low-band signal referred to by SBR is narrowed and
thus there is little point in allocating large code amount to the
coded high-band signal 254. As a result, as shown in (b) of FIG. 9,
the reproduction band of the signal which is reproduced by the
audio signal decoding device 300 is not significantly compromised.
For example, compared to the example shown in FIG. 4, although the
reproduction band in the time slot 3 shown in FIG. 9 is similar to
the time slot where the transmission capacity is small shown in
FIG. 4, the total code amount is less than that shown in FIG. 4. In
other words, a decrease in reproduction band when the bitrate is
lowered is reduced.
[0119] In a time slot 4, the transmission capacity of the
transmission path 400 is further scarce. As a result, the actual
transmission capacity is less than the transmission capacity
estimated by the transmission capacity estimation unit 203.
[0120] Here, as described above, the transmission path 400 has
functionality of discarding a signal on a low priority layer when
the amount of transmission exceeds a predetermined value.
Therefore, in this case, the coded high-band signal 254 which is
allocated to the low priority layer of the transmission path 400
and transmitted is discarded, in which case, the high-band signal
decoding unit 312 included in the audio signal decoding device 300
generates, as the decoded high-band signal 355, a zero signal or a
signal which mimics a high-band signal. As a result, the
reproduction band of a signal which is reproduced by the audio
signal decoding device 300 is compromised as shown in (b) FIG. 9,
but audio discontinuities or the like which are due to scarceness
of the transmission capacity do not occur.
[0121] In the following, the process flows by the audio signal
coding device 200 and the audio signal decoding device 300 will be
described.
[0122] FIG. 10 is a flowchart illustrating the audio signal coding
process performed by the audio signal coding device 200.
[0123] First, the transmission capacity estimation unit 203
estimates transmission capacity of the transmission path 400
(S101).
[0124] Next, the layer boundary setting unit 204 determines a
coding bitrate to be used by the layered coding unit 201 for signal
coding, according to the estimated transmission capacity (S102).
The layer boundary setting unit 204 also determines the layer
boundary (the boundary frequency), based on the determined coding
bitrate (S103). Moreover, the layer boundary setting unit 204
generates the boundary information 255 which indicates the
determined layer boundary.
[0125] Next, the splitter unit 211 splits the input audio signal
250 at the layer boundary determined in step S103 to generate the
low-band signal 251 and the high-band signal 252 (S104).
[0126] Next, the low-band signal coding unit 212 codes the low-band
signal 251 to generate the coded low-band signal 253. The high-band
signal coding unit 213 codes the high-band signal 252 to generate
the coded high-band signal 254 (S105).
[0127] Next, the multiplexer unit 202 multiplexes the coded
low-band signal 253, the coded high-band signal 254, and the
boundary information 255 to generate the coded audio signal 260
(S106). Last, the multiplexer unit 202 transmits the coded audio
signal 260 generated in step 106 through the transmission path 400
(S107).
[0128] FIG. 11 is a flowchart illustrating the audio signal
decoding process performed by the audio signal decoding device
300.
[0129] First, the splitter unit 301 receives the coded audio signal
260 transmitted through the transmission path 400 (S201).
[0130] Next, the splitter unit 301 determines whether the coded
audio signal 260 includes the coded high-band signal 352
(S202).
[0131] If the coded audio signal 260 includes the coded high-band
signal 352 (Yes in S202), the splitter unit 301 obtains the coded
low-band signal 351, the coded high-band signal 352, and the
boundary information 353 that are included in the coded audio
signal 260 (S203).
[0132] Next, the layered decoding unit 302 decodes the coded
low-band signal 351 and the coded high-band signal 352 according to
the layer boundary (the boundary frequency) indicated by the
boundary information 353, to generate the decoded low-band signal
354 and the decoded high-band signal 355 (S204).
[0133] Next, the combiner unit 313 combines the decoded low-band
signal 354 and the decoded high-band signal 355 to generate the
decoded audio signal 350 (S205).
[0134] In contrast, if the coded audio signal 260 does not include
the coded high-band signal 352 (No in S202), the splitter unit 301
obtains the coded low-band signal 351 included in the coded audio
signal 260 (S206).
[0135] Next, the layered decoding unit 302 decodes the coded
low-band signal 351 to generate the decoded low-band signal 354
(S207).
[0136] Next, the combiner unit 313 generates the decoded audio
signal 350, using the decoded low-band signal 354 (S208).
[0137] As described above, the audio signal coding device 200
according to the present embodiment changes the boundary frequency
used in signal splitting, in response to a transmission capacity of
the transmission path 400. Specifically, if the transmission
capacity is large, the audio signal coding device 200 sets the
boundary frequency high, and if the transmission capacity is small,
sets the boundary frequency low. This allows the audio signal
coding device 200 to appropriately correspond to the variation in
transmission capacity of the transmission path 400.
[0138] As such, the audio signal coding device 200 can switch the
coding bitrate in response to the transmission capacity even if the
layered coding scheme in which the frequency band is split and
coded is employed in environment where the transmission capacity of
the transmission path 400 varies from time to time. Moreover, the
audio signal coding device 200 can inhibit the decrease in
reproduction band when the coding bitrate is lowered. Furthermore,
even if the transmission capacity of the transmission path 400 is
further scarce, the audio signal coding device 200 discards a
high-band signal, thereby reducing the bitrate.
EMBODIMENT 2
[0139] In the embodiment 1 described above, the number of channels
of the input audio signal 250 is not particularly limited. The
input audio signal 250 may be a 1-channel signal, 2-channel signal,
5.1-channel signal, 7.1-channel signal, or be of any other number
of channels. The above-described processing may be implemented in
response to each channel signal.
[0140] Meanwhile, to further correspond to the variation in
transmission capacity of the transmission path, that is, to ensure
no audio discontinuities occur even if the transmission capacity is
further scarce, a technique may be applied which upmixes a
downmixed signal using correlation between channels.
[0141] The present embodiment will describe the case where such
downmixing and upmixing are performed.
[0142] FIG. 12 is a block diagram of an audio signal coding device
200A according to the present embodiment. It should be noted that
the same reference signs as those in FIG. 6 will be used in FIG. 12
to refer to the same components, and a difference of the present
embodiment from the embodiment 1 will be mainly described
below.
[0143] The audio signal coding device 200A shown in FIG. 12
includes an inter-channel correlation detection unit 221 and a
downmix unit 222, in addition to the configuration of the audio
signal coding device 200 shown in FIG. 6. The audio signal coding
device 200A includes a multiplexer unit 202A which is different in
functionality from the multiplexer unit 202.
[0144] The audio signal coding device 200A codes an input audio
signal 250A to generate a coded audio signal 260A. The input audio
signal 250A is an N-channel audio signal (where N is an integer
greater than 1), for example, a 7.1-channel signal or a 5.1-channel
signal.
[0145] The inter-channel correlation detection unit 221 detects a
phase difference between channels of the N-channel input audio
signal 250A and a ratio between levels of the channels, and
generates inter-channel correlation information 271 indicative of
the phase difference and the ratio between the levels.
[0146] Using the inter-channel correlation information 271, the
downmix unit 222 downmixes the N-channel input audio signal 250A
into an M-channel signal (M<N) to generate a downmix signal 272.
For example, the downmix unit 222 downmixes a 7.1-channel signal or
a 5.1-channel signal into a 2-channel signal or a 1-channel signal.
The downmix unit 222 may downmix a 2-channel signal into a
1-channel signal.
[0147] Examples of the inter-channel correlation information 271
include a phase difference information or gain ratio information
between the channels, i.e., information standardized by MPEG
standards MPEG surround scheme.
[0148] It should be noted that the layered coding unit 201 performs
the same operation on the downmix signal 272 as performed on the
above-described input audio signal 250.
[0149] The multiplexer unit 202A multiplexes the inter-channel
correlation information 271, in addition to the coded low-band
signal 253, the coded high-band signal 254, and the boundary
information 255, to generate the coded audio signal 260A.
[0150] FIG. 13 is a block diagram of the audio signal decoding
device 300A which decodes the coded audio signal 260A. It should be
noted that the same reference signs as those in FIG. 7 will be used
in FIG. 13 to refer to the same components, and a difference of the
present embodiment from the embodiment 1 will be mainly described
below.
[0151] The audio signal decoding device 300A shown in FIG. 13
includes an upmix unit 321, in addition to the configuration of the
audio signal decoding device 300 shown in FIG. 7. The audio signal
decoding device 300A includes a splitter unit 301A which is
different in functionality from the splitter unit 301.
[0152] The audio signal decoding device 300A decodes the coded
audio signal 260A to generate the decoded audio signal 350A.
[0153] In addition to the functionality of the splitter unit 301
described above, the splitter unit 301A splits inter-channel
correlation information 361 from the coded audio signal 260A and
sends it to the upmix unit 321. The inter-channel correlation
information 361 corresponds to the inter-channel correlation
information 271 generated by the audio signal coding device
200A.
[0154] The upmix unit 321 upmixes the M-channel decoded audio
signal 350 into the N-channel decoded audio signal 350A (N>M),
using, for example, the phase difference information between
channels or the gain ratio information between the channels
indicated by the inter-channel correlation information 271. This
method of upmixing is standardized by MPEG standards MPEG surround
scheme, for example.
[0155] Here, the multiplexer unit 202A allocates the inter-channel
correlation information 271 to a low priority layer of the
transmission path 400, as with the coded high-band signal 254. This
may result in further reduction in bitrate by dropping the
inter-channel correlation information 271 when the transmission
capacity of the transmission path 400 is scarce. This no longer
allows upmixing of the number of channels but avoids occurrence of
audio discontinuities.
[0156] In the following, the process flows by the audio signal
coding device 200A and the audio signal decoding device 300A will
be described.
[0157] FIG. 14 is a flowchart illustrating the audio signal coding
process performed by the audio signal coding device 200A. It should
be noted that the same reference signs as those in FIG. 10 will be
used in FIG. 14 to refer to the same components, and a difference
of the present embodiment from the embodiment 1 will be mainly
described below.
[0158] The processing illustrated in FIG. 14 further includes steps
S111 and S112, in addition to the steps included in the processing
illustrated in FIG. 10. The processing illustrated in FIG. 14
includes step S106A in place of step S106.
[0159] First, the inter-channel correlation detection unit 221
detects a phase difference between channels of the N-channel input
audio signal 250A and a ratio of levels between the channels, and
generates the inter-channel correlation information 271 indicative
of the phase difference and the ratio of the levels (S111).
[0160] Next, using the inter-channel correlation information 271
the downmix unit 222 downmixes the N-channel input audio signal
250A into an M-channel signal (M<N) to generate the downmix
signal 272 (S112). It should be noted that steps S101 to S105 are
the same as those illustrated in FIG. 10.
[0161] Next, the multiplexer unit 202A multiplexes the coded
low-band signal 253, the coded high-band signal 254, the boundary
information 255, and the inter-channel correlation information 271
to generate the coded audio signal 260A (S106A).
[0162] FIG. 15 is a flowchart illustrating the audio signal
decoding process performed by the audio signal decoding device
300A. It should be noted that the same reference signs as those in
FIG. 11 will be used in FIG. 15 to refer to the same processes, and
a difference of the present embodiment from the embodiment 1 will
be mainly described below.
[0163] The processing illustrated in FIG. 15 further includes step
S210, in addition to the steps included the processing illustrated
in FIG. 11. The processing illustrated in FIG. 15 includes step
S203A in place of step S203.
[0164] If the coded audio signal 260A includes the coded high-band
signal 352 (Yes in S202), the splitter unit 301 obtains the coded
low-band signal 351, the coded high-band signal 352, the boundary
information 353, and the inter-channel correlation information 361
which are included in the coded audio signal 260 (S203A). It should
be noted that steps S204 and S205 are the same as those illustrated
in FIG. 11.
[0165] Next, the upmix unit 321 upmixes the M-channel decoded audio
signal 350 using the inter-channel correlation information 361 to
generate the N-channel decoded audio signal 350A (S210).
[0166] The audio signal coding device and audio signal decoding
device according to the embodiments of the present disclosure have
been described. The present disclosure, however, is not limited to
the embodiments.
[0167] Moreover, the processing components included in the audio
signal coding device and the audio signal decoding device according
to the embodiments described above are each implemented typically
in an LSI (Large Scale Integration) which is an integrated circuit.
These processing components may separately be mounted on one chip,
or some or the whole of the processing components may be mounted on
one chip.
[0168] Moreover, the integrated circuit is not limited to the LSI,
and may be implemented in a dedicated circuit or a general-purpose
processor. A field programmable gate array (FPGA) that can be
programmed after manufacturing the LSI or a reconfigurable
processor in which connection or settings of circuit cells in LSI
is reconfigurable may be used.
[0169] Moreover, each component in each embodiment may take a form
of dedicated hardware or may be implemented by executing a software
program suitable for the component. Alternatively, the component
may be implemented by a program execution unit, such as a CPU or
processor, loading and executing the software program stored in a
recording medium such as a hard disk or a semiconductor memory.
[0170] Furthermore, the present disclosure may be the
above-described program or a non-transitory computer-readable
storage medium having stored therein the program. Moreover, the
program can, of course, be distributed via a transmission medium
such as the Internet.
[0171] Moreover, at least some of the functionality of the audio
signal coding device and audio signal decoding device according to
the embodiments 1 and 2 and variations thereof may be combined.
[0172] Moreover, numerals used in the above are merely illustrative
for specifically describing the present disclosure and the present
disclosure is not limited thereto. The connection between the
components is merely illustrative for specifically describing the
present disclosure and connection implementing the functionality of
the present disclosure is not limited thereto.
[0173] Moreover, the division of the functional blocks in the block
diagrams is merely illustrative. A plurality of functional blocks
may be implemented in one functional block, one functional block
may be divided into plural, or some function of one functional
block may be transferred to another. Similar function of a
plurality of functional blocks may be processed in parallel or in a
time sharing manner by a single piece of hardware or software.
[0174] Moreover, the order in which the steps included in the audio
signal coding method and the audio signal decoding method is merely
illustrative for specifically describing the present disclosure and
may be different order. Some of the steps described above may be
executed concurrently (in parallel) with other steps.
[0175] Furthermore, the present embodiments carried out in various
ways that may be conceived by those skilled in the art are included
in the present disclosure, without departing from the spirit of the
present disclosure.
[0176] Although only some exemplary embodiments of the present
disclosure have been described in detail above, those skilled in
the art will readily appreciate that many modifications are
possible in the exemplary embodiments without materially departing
from the novel teachings and advantages of the present disclosure.
Accordingly, all such modifications are intended to be included
within the scope of the present disclosure.
INDUSTRIAL APPLICABILITY
[0177] The present disclosure is applicable to audio signal coding
devices and audio signal decoding devices. The present disclosure
is also suited for a transmitting device and a receiving device for
an AV signal over a digital network.
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